Photoelectric Effect

1 Mark Questions

1. Define intensity of radiation on the basis of photon picture of light. Write its SI unit.

[All India 2014]

Ans. The intensity of radiation is defined as the rate of emitted energy from unit surface area through unit solid angle.

Its SI unit is <math>W/m^2</math> sr-<math>^1</math>.

1. The graph shows the variation of stopping potential with frequency of incident radiation for

two photosensitive metals A and B. Which one of the two has higher value of work-function? Justify your answer. [All India 2014]

Metal B Metal A

Stopping potential <math>(V_0)</math> 0 <math>v_0</math> <math>v_0</math> <math>\frac{W_0}{e}</math> Frequency of — incident radiation (v) <math>\frac{W_0'}{e}</math>

Ans. Metal A has higher value of work-function because and the intercept of the line of the given graph depends on work-function.

1. The graph shows variation of stopping potential <math>V_0</math> versus frequency of incident radiation <math>\nu</math>

for two photosensitive metals A and Which one of the two metals has higher threshold frequency and why? [All India 2014]

Metal B Metal A Stopping potential <math>(V_0)</math> <math>\mathbf{v}_{0}</math> 0 <math>\frac{W_0}{e}</math> incident radiation (v) Frequency of ---- <math>\frac{W_0}{e}</math>

Ans.

<math>V_0</math> Metal B Metal A .

O Ρ Q ٧ As <math display="block">OQ > OP</math> :. <math>v_0' > v_0</math> (1) So, the threshold frequency of metal A is greater than metal B.